The present invention relates to retinoic acid receptor (xe2x80x9cRARxe2x80x9d) selective retinoid agonists, pharmaceutical compositions containing such RAR agonists, to the use of such retinoic acid receptor agonists, particularly retinoic acid receptor xcex3 (RARxcex3) selective agonists, for the treatment of emphysema and related pulmonary diseases. More specifically, the invention is directed to retinoic acid receptor agonists of formula I 
wherein X, R, R1 and m are as defined below, and pharmaceutical compositions containing such compounds.
Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality, ranking third and fourth as the leading cause of death in the European Union and North America respectively. COPD is characterized by reduced maximum expiratory flow, which does not change over several months and which persists for 2 or more consecutive years. Patients with the most severe form of COPD generally present with a significant degree of emphysema. Emphysema is defined anatomically by permanent airspace enlargement distal to the terminal bronchioles. It is characterized by gradual loss of lung recoil, alveolar destruction, decreased alveolar surface area and gas exchange, leading to a reduced FEV1. These two features, impaired gas exchange and reduction in,expiratory flow, are characteristic physiological abnormalities from which patients with emphysema suffer. The main symptom of patients with severe emphysema is shortness of breath during minimal physical activity.
The most common cause of emphysema is cigarette smoking, although other potential environmental toxins may also contribute to the disease. These various insulting agents activate destructive processes in the lung, including release of active proteases and free radical oxidants in excess of protective mechanisms. The imbalance in protease/anti-protease levels leads to destruction of the elastin matrix, loss of elastic recoil, tissue damage and continuous decline in lung function. Avoiding injurious agents (i.e. cessation of smoking) slows the rate of damage. However, the damaged alveolar structures do not regenerate and to the extent lung function is lost, it is not regained.
Retinoic acid is a multifunctional modulator of cellular behavior, having the potential to alter both extracellular matrix metabolism and normal epithelial differentiation. In lung, retinoic acid has been shown to modulate various aspects of lung differentiation by interacting with specific retinoic acid receptors (RAR) that are selectively expressed temporally and spatially. Coordinated activation of RARxcex2 and RARxcex3 has been associated with lung branching and alveolization/septation. During alveolar septation, retinoic acid storage granules increase in the fibroblastic mesenchyme surrounding alveolar walls and RARxcex3 expression in the lung peaks. Depletion of these retinyl-ester stores parallels the deposition of new elastin matrix and septation. It has been demonstrated that postnatal administration of retinoic acid increases the number of alveoli in rats. See Massaro et al., Am. J. Physiol., 1996, 270, L305-L3 10. Furthermore, the capacity of dexamethasone to prevent the expression of CRBP and RARxcex2 mRNA and subsequent alveolar septation in developing rat lungs was abrogated by all-trans retinoic acid.
Recent studies have shown that all-trans retinoic acid can induce formation of new alveoli and return elastic recoil to near normal in animal models of emphysema (D. Massaro et al. Nature Medicine, 1997, 3, 675). However, the mechanism by which this occurs remains unclear.
Retinoids are a class of compounds structurally related to vitamin A, comprising natural and synthetic compounds. Several series of retinoids have been found clinically useful in the treatment of dermatological and oncological diseases. Retinoic acid and its other naturally occurring retinoid analogs (9-cis retinoic acid, all-trans 3,4-didehydro retinoic acid, 4-oxo retinoic acid and retinol) are pleiotropic regulatory compounds that modulate the structure and function of a wide variety of inflammatory, immune and structural cells. They are important regulators of epithelial cell proliferation, differentiation and morphogenesis in lungs. Retinoids exert their biological effects through a series of hormone nuclear receptors that are ligand inducible transcription factors belonging to the steroid/thyroid receptor superfamily. The retinoid receptors are classified into two families, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), each consisting of three distinct subtypes (xcex1,xcex2, and xcex3). Each subtype of the RAR gene family encodes a variable number of isoforms arising from differential splicing of two primary RNA transcripts. All-trans retinoic acid is the physiological hormone for the retinoic acid receptors and binds with approximately equal affinity to all the three RAR subtypes, but does not bind to the RXR receptors for which 9-cis retinoic acid is the natural ligand.
In many non-pulmonary tissues, retinoids have anti-inflammatory effects, alter the progression of epithelial cell differentiation, and inhibit stromal cell matrix production. These properties have led to the development of topical and systemic retinoid therapeutics for dermatological disorders such as psoriasis, acne, and hypertrophic cutaneous scars. Other applications include the control of acute promyelocytic leukemia, adeno- and squamous cell carcinoma, and hepatic fibrosis. A limitation in the therapeutic use of retinoids outside of cancer has stemmed from the relative toxicity observed with the naturally occurring retinoids, all-trans retinoic acid and 9-cis retinoic acid. These natural ligands are non-selective and therefore have pleiotropic effects throughout the body, which are often toxic. Recently various retinoids have been described that interact selectively or specifically with the RAR or RXR receptors or with specific subtypes (xcex1,xcex2,xcex3) within a class.
Thus, in addition to their use in the treatment of emphysema and other pulmonary diseases, the retinoids of the invention are useful in the therapy, amelioration, and prophylaxis of dermatological disorders which are accompanied by epithelial lesions, e.g. acne and psoriasis, light- and age-damaged skin; as well as for the promotion of wound healing, for example of incised wounds, such as surgical wounds, wounds caused by burns and other wounds caused by cutaneous trauma; and for the therapy and prophylaxis of malignant and premaligant epithelial lesions, tumors and precancerous changes of the mucous membrane in the mouth, tongue, larynx, oesophagus, bladder, cervix and colon.
In one embodiment, the present invention is directed toward new RAR selective retinoid agonists of formula 
wherein
R is selected from the group consisting of hydrogen, alkyl, alkoxy, benzyl and phenethyl;
R1 is hydrogen or alkyl;
X is C(R2R3) and m is an integer 1, 2 or 3, or alternatively, X is oxygen, sulfur or NH and m is 1; and
R2, and R3 are each independently selected from hydrogen and lower alkyl; and pharmaceutically acceptable salts of the carboxylic acids of compounds of formula I.
The term xe2x80x9calkylxe2x80x9d as used herein denotes straight chain or branched alkyl residues containing 1 to 10, preferably 1 to 7, carbon atoms, such as methyl, ethyl, isobutyl, pentyl, amyl, 3-pentyl, hexyl, heptyl and the like. The term xe2x80x9clower alkylxe2x80x9d as used herein denotes alkyl residues as defined above, but having 1 to 5 carbon atoms.
As used herein, the term xe2x80x9calkoxyxe2x80x9d refers to a straight or branched chain hydrocarbonoxy group wherein the xe2x80x9calkylxe2x80x9d portion is an alkyl group as defined above. Examples include methoxy, ethoxy, n-propyloxy and the like.
The term xe2x80x9cpharmaceutically acceptablexe2x80x9d such as pharmaceutically acceptable carrier, excipient, salt, etc., means pharmacologically acceptable and substantially non-toxic to the subject to which the particular compound is administered.
The compounds of formula I wherein R1 is hydrogen form salts with pharmaceutically acceptable bases such as alkali salts, e.g. Na- and K-salts, or ammonium or substituted ammonium salts such as trimethylammonium salts, all of which are contemplated in this invention.
Preferred compounds of formula I are compounds wherein X is C(R2R3) and m is 2. Particularly preferred compounds are those wherein R1, R2 and R3 are hydrogen and R is alkyl selected from pentyl and hexyl, for example, the following compounds:
(E)-5-[2-(3-hexyl-5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-naphthalen-2-yl)-vinyl]-thiophene-2-carboxylic acid; and
(E)-5-[2-(3-pentyl-5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-naphthalen-2-yl)-vinyl]-thiophene-2-carboxylic acid.
The compounds of formula I can be prepared according to synthetic scheme 1 below. The starting material 5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene, compound 1, can be prepared in accordance to the teachings of U.S. Pat. No. 4,123,469. compound 1 is subjected to a Friedels-Kraft acylation, followed by a reduction of the carbonyl under H2 atmosphere in presence of Pd/C, giving the intermediate 2 in high yield. 
wherein X, R and R1 and m are as defined above.
Bromination of compound 2 under Br2/Fe provided compound 3, which when treated with BuLi and of N,N-dimethylformamide (DMF), yields the aldehyde compound 4. Reduction of compound 4 in the presence of BH3.THF, at 0xc2x0 C., yields alcohol 5. Bromination of compound 5 at the benzylic position (CBr4/Ph3P) yields compound 6. The phosphonium salt 7, is then obtained by treatment of compound 6 with Ph3P in refluxing toluene. A Wittig reaction of 5-formyl-2-thiophene carboxylic methyl ester with the phosphonium salt compound 7 yields olefin compound 8 in good yield with a cis/trans ratio 1:14.
Isomer separation can be achieved by using a medium pressure liquid chromatography (MPLC). The desired ester of E configuration can then be hydrolysed under standard conditions to the corresponding acid, i.e. the compound of formula I, wherein R1 is hydrogen.
Alternatively, compounds of formula I may be prepared pursuant to Scheme 2 below. 
The aldehyde 4 is reacted with the appropriate phosphonate in a Wittig-Horner reaction. The olefin thus obtained (compound 8) is almost exclusively of E geometry. Hydrolysis under standard conditions known in the art and recrystallization provides the compounds of formula I wherein R1 is hydrogen, and with exclusive E-symmetry double bond.
Compounds of formula I wherein X is oxygen, sulfur or NH and m is 1 can be prepared by analogy to the method described above, starting from the corresponding 2,3-dihydro-1H-isoindole, 1,3-dihydro-benzo[c]thiophen and 1,3-dihydro-benzofuran, respectively (Tetrahedron, 1992, 48, 10569; Aust. J. Chem., 1983, 36, 397).
This invention is also directed to a method for treating or controlling emphysema and associated pulmonary diseases by administering to a patient in need of such treatment a therapeutically effective amount of a RAR selective agonist of formula I. Systemic administration of compounds of formula I is the preferred mode of delivery.
As used herein, a xe2x80x9ctherapeutically effective amountxe2x80x9d means an amount of a compound that, when administered to a mammal, particularly a human patient, for treating, preventing, controlling, or ameliorating a disease is sufficient to effect such treatment, prevention, control, or amelioration of the disease. The xe2x80x9ctherapeutically effective amountxe2x80x9d will vary depending on the compound, the disease and its severity, and the age, weight, etc., of the mammal to be treated. A typical dose of a compound of formula I is between about 1 and about 100 xcexcg/kg body weight per day, preferably from about 5 to about 50 xcexcg/kg body weight per day.
The RARxcex3 agonist selectivity of a compound can be determined by routine ligand binding assays known to those skilled in the art, for example, the assays described in C. Apfel etal. Proc. Nat. Sci. Acad. (USA), 89:7129-7133 (1992); M. Teng et al., J. Med. Chem. 40:2445-2451 (1997); and PCT Publication WO 96/30009.
Treatment with RAR agonists, particularly RARxcex3 selective agonists, is useful to promote repair of alveolar matrix and septation. Thus, the RAR agonists taught in this invention are useful for promoting the repair of damaged alveoli and septation of new alveoli, particularly for the treatment emphysema.
The particular dosage of a RAR selective agonist of formula I required to treat lung emphysema is dependant on the severity of the condition. This dosage may be delivered in a conventional pharmaceutical composition by a single administration, by multiple applications, or via controlled release, as needed to achieve the most effective results. Dosing will continue for as long as is medically indicated, which depending on the severity of the disease may range from a few weeks to several months.
This invention is also directed to pharmaceutical compositions containing compounds of formula I and a pharmaceutically acceptable carrier, excipient and/or diluent. Typical pharmaceutically acceptable compositions, of an RAR agonist of formula I include the salts of such compounds and a pharmaceutically acceptable carrier. In the context of the present invention, xe2x80x9cpharmaceutically acceptable saltsxe2x80x9d include any chemically suitable salt known in the art of retinoid agonists as applicable for administration to human patients. Examples of conventional salts known in the art include the alkali metal salts such as sodium and potassium salts, the alkaline earth metal salts such as calcium and magnesium salts, and ammonium and alkyl ammonium salts.
Representative delivery regimens include oral, parenteral (including subcutaneous, intramuscular and intravenous), rectal, buccal (including sublingual), transdermal, pulmonary and intranasal. One method of pulmonary administration involves aerosolization of a solution of an RAR agonist. Aerosolized compositions may include the compound packaged in reverse micelles or liposomes. Typical pulmonary and respiratory delivery systems are described in U.S. Pat. Nos. 5,607,915, 5,238,683, 5,292,499, and 5,364,615.
The treatment methods of this invention also include systemic administration of RAR agonists in simultaneous or sequential combination with one or more additional active ingredients.
The RAR agonists of the invention typically will be administered as pharmaceutical compositions in admixture with a pharmaceutically acceptable carrier. As mentioned above, such compositions may be prepared for parenteral (subcutaneous, intramuscular or intravenous) administration, particularly in the form of liquid solutions or suspensions; for oral or buccal administration, particularly in the form of tablets or capsules; for intranasal administration, particularly in the form of powders, nasal drops or aerosols; and for rectal or transdermal administration. Any conventional carrier material can be employed. Suitable pharmaceutically acceptable carriers include organic or inorganic carrier materials, such as water, gelatin, gum arabic, lactose, starch, magnesium stearate, talc, polyalkylene glycols, petroleum jelly and the like.
Liquid formulations for parenteral administration may contain as excipients sterile water or saline, alkylene glycols such as propylene glycol, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, hydrogenated naphthalenes and the like. They may employ slightly acidic buffers in pH ranges of about 4 to about 6. Suitable buffers include acetate, ascorbate and citrate at concentrations ranging from about 5 mM to about 50 mM. For oral administration, the formulation can be enhanced by the addition of bile salts or acylcarnitines.
Formulations for nasal administration may be solid and may contain excipients, for example, lactose or dextran, or may be aqueous or oily solutions for use in the form of nasal drops or metered spray. Particular nasal formulations include dry powders suitable for conventional dry powder inhalers (DPI""s), liquid solutions or suspensions suitable for nebulization and propellant formulations suitable for use in metered dose inhalers (MDI""s). For buccal administration typical excipients include sugars, calcium stearate, magnesium stearate, pregelatinated starch, and the like.
In formulations for nasal administration, the absorption across the nasal mucous membrane may be enhanced by inclusion of surfactant acids, such as for example, glycocholic acid, cholic acid, taurocholic acid, ethocholic acid, deoxycholic acid, chenodeoxycholic acid, dehydrocholic acid, glycodeoxycholic acid, cyclodextrins and the like in an amount in the range between about 0.2 and 15 weight percent, preferably between about 0.5 and 4 weight percent, most preferably about 2 weight percent.
Solid forms for oral administration include tablets, hard and soft gelatin capsules, pills, sachets, powders, granules and the like. Each tablet, pill or sachet may contain from about 1 to about 50 mg, preferably from 5 to about 10 mg of RAR agonist. Preferred solid oral dosage forms include tablets, two-piece hard shell capsules and soft elastic gelatin (SEG) capsules. SEG capsules are of particular interest because they provide distinct advantages over the other two forms (see Seager, H., xe2x80x9cSoft gelatin capsules: a solution to many tableting problemsxe2x80x9d; Pharmaceutical Technology, 9, (1985). Some of the advantages of using SEG capsules are: a) dose-content uniformity is optimized in SEG capsules because the drug is dissolved or dispersed in a liquid that can be dosed into the capsules accurately b) drugs formulated as SEG capsules show good bioavailability because the drug is dissolved, solubilized or dispersed in an aqueous-miscible or oily liquid and therefore when released in the body the solutions dissolve or are emulsified to produce drug dispersions of high surface area and c) degradation of drugs that are sensitive to oxidation during long-term storage is prevented because of the dry shell.
Delivery of the compounds of the present invention to a patient over prolonged periods of time, for example, for periods of from one week to one year, may be accomplished by a single administration of a controlled release system containing sufficient active ingredient of formula I for the desired release period. Various controlled release systems, such as monolithic or reservoir type microcapsules, depot implants, osmotic pumps, vesicles, micelles, liposomes, transdermal patches, iontophoretic devices and alternative injectable dosage forms may be utilized for this purpose. Localization at the site to which delivery of the active ingredient is desired is an additional feature of some controlled release devices, which may prove beneficial in the treatment of certain disorders.
The following are representative pharmaceutical formulations for using RAR selective agonists as described herein for promoting elastin mediated matrix repair and alveolar septation.
The following ingredients are mixed thoroughly and pressed into single scored tablets.
The following ingredients are mixed thoroughly and loaded into a hard-shell gelatin capsule.
The following ingredients are mixed to form a suspension for oral administration.
The following ingredients are mixed to form an injectable formulation.
The following ingredients are mixed to form a suspension for nasal administration.